Re: [PATCH v3 1/6] ebpf: Added eBPF map update through mmap.

[Daniel P . Berrangé]

On Thu, Jun 15, 2023 at 01:10:21AM +0300, Andrew Melnychenko wrote:
> Changed eBPF map updates through mmaped array.
> Mmaped arrays provide direct access to map data.
> It should omit using bpf_map_update_elem() call,
> which may require capabilities that are not present.
> 
> Signed-off-by: Andrew Melnychenko 
> ---
>  ebpf/ebpf_rss.c | 117 ++--
>  ebpf/ebpf_rss.h |   5 +++
>  2 files changed, 99 insertions(+), 23 deletions(-)

Reviewed-by: Daniel P. Berrangé 


With regards,
Daniel
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[PATCH v3 1/6] ebpf: Added eBPF map update through mmap.

[Andrew Melnychenko]

Changed eBPF map updates through mmaped array.
Mmaped arrays provide direct access to map data.
It should omit using bpf_map_update_elem() call,
which may require capabilities that are not present.

Signed-off-by: Andrew Melnychenko 
---
 ebpf/ebpf_rss.c | 117 ++--
 ebpf/ebpf_rss.h |   5 +++
 2 files changed, 99 insertions(+), 23 deletions(-)

diff --git a/ebpf/ebpf_rss.c b/ebpf/ebpf_rss.c
index cee658c158b..247f5eee1b6 100644
--- a/ebpf/ebpf_rss.c
+++ b/ebpf/ebpf_rss.c
@@ -27,19 +27,83 @@ void ebpf_rss_init(struct EBPFRSSContext *ctx)
 {
 if (ctx != NULL) {
 ctx->obj = NULL;
+ctx->program_fd = -1;
+ctx->map_configuration = -1;
+ctx->map_toeplitz_key = -1;
+ctx->map_indirections_table = -1;
+
+ctx->mmap_configuration = NULL;
+ctx->mmap_toeplitz_key = NULL;
+ctx->mmap_indirections_table = NULL;
 }
 }
 
 bool ebpf_rss_is_loaded(struct EBPFRSSContext *ctx)
 {
-return ctx != NULL && ctx->obj != NULL;
+return ctx != NULL && (ctx->obj != NULL || ctx->program_fd != -1);
+}
+
+static bool ebpf_rss_mmap(struct EBPFRSSContext *ctx)
+{
+if (!ebpf_rss_is_loaded(ctx)) {
+return false;
+}
+
+ctx->mmap_configuration = mmap(NULL, qemu_real_host_page_size(),
+   PROT_READ | PROT_WRITE, MAP_SHARED,
+   ctx->map_configuration, 0);
+if (ctx->mmap_configuration == MAP_FAILED) {
+trace_ebpf_error("eBPF RSS", "can not mmap eBPF configuration array");
+return false;
+}
+ctx->mmap_toeplitz_key = mmap(NULL, qemu_real_host_page_size(),
+   PROT_READ | PROT_WRITE, MAP_SHARED,
+   ctx->map_toeplitz_key, 0);
+if (ctx->mmap_toeplitz_key == MAP_FAILED) {
+trace_ebpf_error("eBPF RSS", "can not mmap eBPF toeplitz key");
+goto toeplitz_fail;
+}
+ctx->mmap_indirections_table = mmap(NULL, qemu_real_host_page_size(),
+   PROT_READ | PROT_WRITE, MAP_SHARED,
+   ctx->map_indirections_table, 0);
+if (ctx->mmap_indirections_table == MAP_FAILED) {
+trace_ebpf_error("eBPF RSS", "can not mmap eBPF indirection table");
+goto indirection_fail;
+}
+
+return true;
+
+indirection_fail:
+munmap(ctx->mmap_toeplitz_key, qemu_real_host_page_size());
+toeplitz_fail:
+munmap(ctx->mmap_configuration, qemu_real_host_page_size());
+
+ctx->mmap_configuration = NULL;
+ctx->mmap_toeplitz_key = NULL;
+ctx->mmap_indirections_table = NULL;
+return false;
+}
+
+static void ebpf_rss_munmap(struct EBPFRSSContext *ctx)
+{
+if (!ebpf_rss_is_loaded(ctx)) {
+return;
+}
+
+munmap(ctx->mmap_indirections_table, qemu_real_host_page_size());
+munmap(ctx->mmap_toeplitz_key, qemu_real_host_page_size());
+munmap(ctx->mmap_configuration, qemu_real_host_page_size());
+
+ctx->mmap_configuration = NULL;
+ctx->mmap_toeplitz_key = NULL;
+ctx->mmap_indirections_table = NULL;
 }
 
 bool ebpf_rss_load(struct EBPFRSSContext *ctx)
 {
 struct rss_bpf *rss_bpf_ctx;
 
-if (ctx == NULL) {
+if (ctx == NULL || ebpf_rss_is_loaded(ctx)) {
 return false;
 }
 
@@ -66,10 +130,18 @@ bool ebpf_rss_load(struct EBPFRSSContext *ctx)
 ctx->map_toeplitz_key = bpf_map__fd(
 rss_bpf_ctx->maps.tap_rss_map_toeplitz_key);
 
+if (!ebpf_rss_mmap(ctx)) {
+goto error;
+}
+
 return true;
 error:
 rss_bpf__destroy(rss_bpf_ctx);
 ctx->obj = NULL;
+ctx->program_fd = -1;
+ctx->map_configuration = -1;
+ctx->map_toeplitz_key = -1;
+ctx->map_indirections_table = -1;
 
 return false;
 }
@@ -77,15 +149,11 @@ error:
 static bool ebpf_rss_set_config(struct EBPFRSSContext *ctx,
 struct EBPFRSSConfig *config)
 {
-uint32_t map_key = 0;
-
 if (!ebpf_rss_is_loaded(ctx)) {
 return false;
 }
-if (bpf_map_update_elem(ctx->map_configuration,
-&map_key, config, 0) < 0) {
-return false;
-}
+
+memcpy(ctx->mmap_configuration, config, sizeof(*config));
 return true;
 }
 
@@ -93,27 +161,19 @@ static bool ebpf_rss_set_indirections_table(struct 
EBPFRSSContext *ctx,
 uint16_t *indirections_table,
 size_t len)
 {
-uint32_t i = 0;
-
 if (!ebpf_rss_is_loaded(ctx) || indirections_table == NULL ||
len > VIRTIO_NET_RSS_MAX_TABLE_LEN) {
 return false;
 }
 
-for (; i < len; ++i) {
-if (bpf_map_update_elem(ctx->map_indirections_table, &i,
-indirections_table + i, 0) < 0) {
-return false;
-}
-}
+memcpy(ctx->mmap_indirections_table, indirections_table,
+sizeof(*indirections_table) * len);
 return t